Generally, conventional circular knitting machines employ a driving pinion to engage with a ring gear integrally formed with or mounted onto a latch needle cylinder having thereon latch needles to perform the knitting operation. Due to the clearance between the teeth of the pinion and those of the ring gear, an oscillation will certainly occur at the point the ring gear and pinoin are engaged. Each time any of the latch needles rotates to the position where it is relatively close to the point of engagement i.e., the oscillation source, the oscillation will grow, while each time any of the latch needles rotates to the position where it is relatively far from the oscillation source, the oscillation decreases. This uneven oscillation leads to the occurrence of undesirable horizontal lines on the knitted fabric. Aside from such an uneven oscillation, there are of course still other causes, such as the uneven quality of yarns, mis-adjustment of cams, etc., which will also create the undesirable horizontal lines. Nevertheless, these other causes may be more easily controlled than the uneven oxcillation and have been controlled in actual practice. To prove that the undesirable horizontal lines arise from the uneven oscillation, the inventor has made an experiment with a circular knitting machine of 38 gauge. In the experiment dye was smeared on the yarn entrance of the transmission assembly which was closest to the oscillation source, i.e., the engagement point between a gear wheel and a pinion so that when the yarn entered, the dye marked the yarn. The resulting knitted fabric revealed a dyed track on thick horizontal lines thereof. The same experiment was repeated at another transmission assembly opposite the first transmission assembly, and the dyed track was again seen on thin horizontal lines thereof. To obtain a further proof thereof, the inventor removed the second mentioned transmission assembly and found that the thin horizontal lines disappeared. Therefore, it has been concluded that the greater the source of oscillation of the latch needles the denser will be the undesirable horizontal lines.